1. Field of the Invention
The present invention relates to a display device and a semiconductor device. Specifically, the present invention relates to a display device and a semiconductor device having a semiconductor layer formed by laser beam irradiation.
2. Description of the Related Art
As an element for driving an EL (Electro Luminescence) display device and the like, a thin film transistor (hereinafter referred to as a TFT) is used.
A low temperature process with the use of a glass substrate has been developed for the purpose of manufacturing a TFT in lower cost. In low temperature process, crystallization with the use of a laser beam is generally utilized as a method for manufacturing a crystalline semiconductor film used as a barrier layer of the TFT.
In the TFT manufactured according to the method described above, variation also occurs in an electrical characteristic of the TFT when variation occurs in a laser irradiation condition.
When the electrical characteristic of the TFT varies, there are problems that display unevenness such as brightness unevenness or gradation unevenness occurs in a display image.